The invention relates to a transmission, and more particularly, relates to a transmission that transmits mechanical power from a power source to a transmission shaft with a continuously variable speed ratio.
Manual transmissions and automatic transmissions for use in wheeled vehicles have been well known for many years. The need to control the power reaching the wheels of a vehicle generated by an engine having a limited range of rotational energy occurs in almost every vehicle having wheels. The need to interject controllable gearing between the engine and the wheels has been found necessary to provide the operator with a reasonable vehicle speed range. The present speed, the orientation, and the weight of a vehicle all contribute to the need to more precisely control the amount of power applied to the wheels to obtain a desired speed of the vehicle. As is well known, a heavy stationary vehicle needs a lower gear ratio to obtain movement than does a light vehicle. Many factors contribute to the need to use different gearing including the above three.
Manual shift transmissions are provided in which five or more forward gears can be manually selected by the operator for more precise control over the transmission of engine power to the wheels. Automatic shift transmissions typically provide fewer forward gears than manual shift transmissions but by virtue of separate gears, still provide control over the transmission of power to the wheels. However, in both of these transmission types, discrete gears are used with each gear providing a preselected gear ratio that cannot be changed. These discrete gearing arrangements require that the engine speed be controllable so that the speed of the vehicle can be more precisely controlled.
It has been found that each engine has a particular rotational speed range within which it operates most efficiently. That is, its power output and fuel efficiency are both high at this particular engine rotational speed range, which is typically a higher rate of speed. While it would be desirable to constantly operate the engine within this most efficient engine speed range and merely vary the gearing to enable the vehicle to operate over a large vehicle speed range, such technique is not possible with present discrete geared transmissions. Because of the relatively large separation between adjacent gears, engine speed can vary by over one thousand revolutions per minute (xe2x80x9cRPMxe2x80x9d) as gears are changed, and in some cases much more. In many cases, part of the engine speed range traversed during acceleration and deceleration through the discrete gears includes less efficient engine speeds where fuel efficiency decreases as well as torque and horsepower being degraded in comparison to other engine speeds. Additionally, gears typically have such a large separation that shifting up into a higher gear will undesirably lug the engine unless the engine rotational speed is sufficiently higher. At the same time, increasing the engine speed too high can overspeed and damage the engine. Thus, the operator must constantly be aware of engine speed versus the vehicle speed in order to shift at the appropriate times with a manual shift transmission.
Automatic transmissions have made the process easier, but the operator can still override the automatic shifting process and overspeed the engine causing damage. Additionally, automatic shift transmissions typically, although not always, use fewer forward gears resulting in greater gear ratio separation. In such automatic transmissions, an even greater engine speed range may be traversed than in manual transmissions with a resulting lower fuel efficiency. It would be desirable if engine speed variations were not such a factor in the transmission of power to the drive wheels of the vehicle.
Present transmissions, whether automatic or manual, use discrete gears that interact. When gears in these transmissions are changed, different gears are brought into engagement with each other thereby changing the overall gearing ratio. Large trucks have increased the number of gears to reduce the spacing between the gears; however, there is a practical limit to the number of gears that can be included in a gearbox due to the concomitant size and weight increases that would occur. Vehicle manufacturers continually strive to reduce the weight of the vehicle as it is easier and more fuel efficient to drive a lighter vehicle than a heavier vehicle. Increasing the number of gears of a gearbox to obtain better fuel efficiency can be out balanced by the increase in the weight and size of that gearbox which will actually result in reduced fuel efficiency.
Over many years there have been attempts to provide a continuously variable transmission (xe2x80x9cCVTxe2x80x9d). Such a transmission permits the engine to be set at an optimum rotational speed for horsepower, torque, and fuel efficiency while the gear ratio in the transmission is varied to control the vehicle speed. The concept is attractive in that the engine speed remains fairly constant while the transmission is shifted through its continuously variable speeds to obtain the desired speed of the vehicle. For example, when starting out, the gearshift or transmission lever is first set at a low gear ratio and is advanced through higher gear ratios until the desired vehicle speed is obtained. If the ratio is too high, the engine will lug and the vehicle speed will drop. The transmission lever is then moved to a lower gear ratio until the vehicle speed increases again to the desired speed. The same occurs when going up a hill. The vehicle will slow down going up the hill and the transmission lever must be moved to a lower gear ratio to maintain the desired speed.
However, very few CVT arrangements have proven successful. Previous versions of CVT""s use some type of friction method to control the variable aspect of the transmission which has not been perfected to deliver large amounts of torque and power. In some cases, rubberized steel belts have been used in the CVT. The rubber surface provides the necessary friction to transmit the drive energy while the embedded steel results in stability and a longer life for the belt. While such an approach has been found to be useful in lighter and smaller vehicles, the need to replace the belt at intervals is undesirable. Additionally, such configuration has not proved to be useful in larger vehicles where increased amounts of power are needed. It has been found that the belt has been unable to handle the higher amounts of power put out by larger engines. The belt will slip and wear prematurely. Other approaches, such as toroidal mechanisms, have been tried, but also with only limited success. Demands for more efficient fuel consumption as well as improvements in speed control over vehicles keep an interest alive in developing a continuously variable transmission.
Hence, those skilled in the art have recognized a need for an improved transmission that permits more variability in the gearing ratio without the use of discrete gears. A need has also been recognized for an improved transmission that permits engine speed to remain within an abbreviated range while a wide range of gearing ratios is provided by the transmission. The present invention fulfills these needs and others.
Briefly and in general terms, the present invention is directed to a continuously variable transmission having a continuously variable ratio from input to output. In one aspect, the continuously variable transmission receives input power and transmits that power, and comprises a lay shaft that rotates in response to the input power, a first translation device that translates the rotation of the lay shaft into linear motion, a second translation device having a plurality of linkage locations, the second translation device translating the linear motion received from the first translation device at a selected linkage location into translated rotational motion, the speed of the translated rotational motion being dependent on the linkage location selected, and a transmission shaft that rotates in response to the translated rotational motion. In a more detailed aspect, the continuously variable transmission further comprises a one-way device that couples translated rotational motion in a first direction provided by the second translation device to the transmission shaft thereby causing rotation of the transmission shaft. And in yet a further more detailed aspect, the second translation device translates the linear motion received from the first translation device into translated rotational motion of a first and a second direction. A more detailed aspect includes the one-way device coupling only the translated rotational motion of the first direction provided by the second translation device to the transmission shaft. A yet more detailed aspect in accordance with the invention comprises the continuously variable transmission wherein the one-way device does not couple the rotational motion of the second direction provided by the second translation device to the transmission shaft.
In other aspects in accordance with the invention, the first translation device comprises a crank disposed on the lay shaft that rotates with the lay shaft, and a drive rod connected to the crank, the drive rod providing linear motion in response to rotational motion of the crank. A one-way device couples translated rotational motion in a first direction provided by the second translation device to the transmission shaft thereby causing rotation of the transmission shaft wherein the second translation device comprises an output rod mounted to the one-way device and rotatably disposed about the transmission shaft such that the output rod provides translated rotational motion to the one-way device, wherein the one-way device couples rotational motion of the output rod in the first direction to the transmission shaft, and wherein the drive rod is linked to the output rod at the selected location along the output rod, the selected location controlling the speed of rotation of the output rod.
In further aspects in accordance with the invention, the output rod comprises a drive slot within which the drive rod is located to link with the output rod, the plurality of linkage locations of the drive rod to the output rod occurring within the drive slot, wherein the linkage location of the drive rod within the drove slot determining the speed of rotation of the output rod. A speed control device is provided that selects the linkage location at which the drive rod links to the output rod. Additionally, an actuator device controls the position of the speed control device and thereby controls the selection of the linkage location at which the first translation device is linked to the second translation device.
In yet further aspects, the continuously variable transmission further comprises a plurality of one-way devices disposed so as to couple translated rotational motion of a first direction to the transmission shaft to thereby cause the transmission shaft to rotate, wherein the first translation device comprises a plurality of cranks disposed on the lay shaft that rotate with the lay shaft, wherein the first translation device further comprises a plurality of drive rods connected to the cranks, the drive rods providing linear motion in response to rotational motion of the cranks, wherein the second translation device comprises a plurality of output rods mounted to a plurality of one-way devices, the output rods also rotatably disposed about the transmission shaft, the output rods providing the translated rotational motion, wherein the one-way devices couple the translated rotational motion of the output rods of the first direction to the transmission shaft, and wherein the drive rods are linked to the output rods at selected locations along the output rods, the selected locations controlling the speed of rotation of the output rods. In more detailed aspects, the continuously variable transmission further comprises a speed control device that selects the linkage locations at which the drive rods link to the output rods.
In accordance with the invention, other aspects include a continuously variable transmission 1 further comprising a second lay shaft coupled to the transmission shaft such that the second lay shaft rotates with rotation of the transmission shaft, a third translation device that translates the rotation of the second lay shaft into linear motion, a fourth translation device having a plurality of linkage locations, the fourth translation device translating the linear motion received from the third translation device at a selected linkage location into second translated rotational motion, the speed of the second translated rotational motion being dependent on the linkage position selected on the fourth translation device, a second transmission shaft that rotates in response to rotational motion, and a second one-way device that couples the second translated rotational motion provided by the fourth translation device to the second transmission shaft thereby causing rotation of the second transmission shaft. In a more detailed aspect, the transmission shaft and the second lay shaft are formed of the same shaft.
In accordance with aspects of the invention, there is provided a method of transmitting input power with a continuously variable ratio of input power to output power, comprising rotating a lay shaft in response to the input power, translating the rotational motion of the lay shaft into linear drive motion, translating the linear drive motion into a rotational drive motion, controlling the ratio of the rotational drive motion to the rotation of the lay shaft during the step of translating the linear drive motion into rotational drive motion, and applying the rotational drive motion occurring in a first direction to a transmission shaft thereby causing the transmission shaft to rotate and provide output power. In more detailed aspects, the method further comprises varying the ratio of the rotational drive motion to the rotation of the lay shaft during the step of translating the linear drive motion into rotational drive motion to provide continuously variable output power. The method further comprises rotating a second lay shaft in response to rotation of the transmission shaft, translating the rotational motion of the second lay shaft into second linear drive motion, translating the second linear drive motion into a second rotational drive motion, controlling the ratio of the second rotational drive motion to the rotation of the second lay shaft during the step of translating the second linear drive motion into second rotational drive motion, and applying the second rotational drive motion occurring in a first direction to a second transmission shaft thereby causing the second transmission shaft to rotate and provide output power.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.